As members of the same family (Cactaceae), cactus plants have flowers that look similar to each other. Fruits are similar as well : -) And for foliage, they've got spines.
Hedgehog Cactus flowers (Echinocereus fasciculatus)
Saguaro flowers (Carnegiea gigantea)
State flower of Arizona
Engelmann Prickly Pear flowers (Opuntia engelmannii var. engelmannii)